circumstances can ultimately be so extensively employed carries evidence that power, and wisdom, and design, adequate to all these varied ultimate effects, were exerted in that construction. Such is the view in which we ought to contemplate the eye; and when we so contemplate its structure, and its powers; the simplicity of the arrangement of its parts, and the analogy between it and the other organs of sensation; its adaptation to near as well as distant objects;* the rich and varied treasures of information, for usefulness, and for enjoyment, which it explores and appreciates; and the indication of mind, of intelligence, and affection, which it so expressively reciprocates; we cannot fail to perceive that, were this organ alone submitted to our observation, it would itself demonstrate that it must have been formed by an intelligent Being, and that the Being who formed it must be possessed of infinite power, and wisdom, and goodness. It would demonstrate more, and what is of more immediate importance to us, for it follows as a corollary that God has put forth into active exertion all these attributes to promote the happiness of his creature man. ARTICLE VII. Method of preserving Volatile and Deliquescent Substances. SIR, (To Dr. Thomson.) Edinburgh, May 11, 1817. EVERY person concerned in chemical operations must have experienced inconvenience from the difficulty of retaining volatile, deliquescent, and efflorescent substances in a state of perfect preservation. Lagrange directs that no volatile acid should stand in that department of a laboratory which is appropriated to the more delicate experiments. Though the stopper of a phial be ever so well ground, it yields to the expansion of the contained substance, occasioned by slight elevations of temperature. In hot climates ether is generally kept in stopped bottles immersed in water in an inverted state; and I believe it will seldom be found that water long thus employed is entirely free from an impregnation of the ether. For obviating these inconveniences, I beg leave to propose the following expedient:-Let every bottle intended for such substances have a circular rim round its shoulder, not rising quite so high as the mouth of the bottle. In the cavity formed by this rim let a quantity of mercury be contained, and let an inverted glass cup, The grey drone fly is said to have 14,000 eyes, and the dragon fly a great many more; but how imperfect is the information obtained by these vast aggre gates of visual orbs compared to the information communicated by the pair be stowed on man. 30 Preservation of Volatile and Deliquescent Substances. [JULY, the mouth of which is adapted to the cavity, be immersed in the mercury covering the stopper and neck of the bottle. The cup, from its lightness compared to the mercury, and from the resistance opposed by the air contained in it, is prevented from sinking to a sufficient depth. The bottom of it, therefore, may be loaded with a flat piece of metal cemented to it. When put on, it should be pressed down, and held a little on one side, for the expulsion of a small part of the air. This pure object may be obtained to any requisite degree by gently warming the cup. It is scarcely necessary to enumerate the advantages which will arise from the adoption of this plan. Volatile acids may stand in any room without in the least endangering the polish of fine metallic surfaces, or affecting the progress of delicate experiments. Those who wish to preserve deliquescent substances in a dry state, as, for example, muriate of lime, or soil which powerfully attracts humidity (substances which, from their cleanliness, are preferable to sulphuric acid for the formation of ice by the process invented by Professor Leslie), may keep them in bottles of this kind. They may also be employed for the preservation of certain minerals, such as extraneous fossils of pyrites, and the lomonite, or mealy zeolite, the preservation of which has occasioned so much unsatisfactory trouble to mineralogists. A similar apparatus may be used for retaining anatomical preparations in spirits, both for preventing more effectually the evaporation of the spirits, and affording greater facility in taking out the preparations at pleasure. The apparatus will be more perfectly understood by an inspection of the annexed figure: A represents the body of the phial: B, B, compartment for mercury: C, C, C, cup inverted in mercury, to keep the phial air-tight; within this are represented the neck and stopper. When the contents of the bottle are wanted, we take off the cup, and, holding the stopper with the finger, begin with pouring out the mercury into the cup, now standing upright on a table. It might be rendered more carriageable by means of a circle of cork passing between A the inverted cup and the containing rim; and still more so by a piece of leather or of bladder tied over the whole, a circular groove being made on the outside of the rim for retaining the string, and the interior surface of the bladder might be smeared with a tenacious substance for confining the mercury. This would contribute to the perfection of the apparatus, if used at sea. But for standing in a room, it will require no such addition, and will then be of itself much more convenient, cleanly, and secure, than the usual expedient of ground stoppers covered with lute. Before concluding, I shall observe that the same principle may be advantageously employed in the construction of domestic implements for preventing the escape of the offensive effluvia of excrementitious substances in the bedchambers of the sick. Pieces of furniture have indeed been made for accomplishing this purpose by means of water used exactly in the same way. But the relative properties of water to the effluvia alluded to are such that these have been justly complained of as ineffectual. I am, Sir, your most obedient servant, HENRY DEWAR. ARTICLE VIII. Report made by M. Poisson of a Memoir by M. Hachette respecting the Running of Liquids through small Orifices, and with Pipes applied to these Orifices.* THE experiments of M. Hachette may be divided into three parts. The object of the first is to measure the contraction of the fluid vein proceeding from a narrow aperture. The second examines the cause of the singular phenomena which take place when small cylindrical or conical pipes are added. In the third part the author describes the figure of the fluid vein, and the variations occasioned by different forms of the orifice. We shall not attempt to explain all the importance of these different questions, either in practice, or as they relate to the theory of the motion of liquids; but, without further preface, we shall give an analysis of the three parts of the memoir subjected to our examination by the Class. PART I.-Contraction of the Fluid Vein. The author examines, in the first place, if the figure of the small orifice has any influence on the quantity of liquid that flows out in a given time. It is generally admitted that, supposing the pressure the same, and the orifice unaltered, the quantity of liquid which flows out is not changed. M. Hachette determines the correctness of this principle when the orifice is circular, triangular, elliptical, or formed of an arch of a circle and two straight lines. But he finds the products very different, either in excess or defect, when the contour of the surface presents re-entering angles, which occasions an important modification in the principle which we have mentioned. If the plane in which it is pierced be not horizontal, the fluid vein forms a curve, which ought to be a parabola corresponding to a certain initial velocity which the author has determined by direct measurement. Setting out from the place of greatest contraction, the thickness becomes constant for a considerable extent; *This memoir was read to the Royal Academy of Sciences, Dec. 18, 1816. namely, tili the jet, by mixing with the air, loses its shape. In this extent all the fluid molecules describe the same curve, and the vein resembles perfectly pure crystal, supposed immoveable. It was, therefore, easy to measure the abscissæ and the ordinates of different points of the same jet; and by a comparison of these measures the author has recognized that the fluid curve does not deviate sensibly from a parabola. He has concluded, likewise, from the known formulas of parabolic motion, the velocity of the fluid in a given point, for example, at the place of greatest contraction. He has found in this manner that the common velocity at all the points of the contracted section is very nearly that derived from the height of the surface above the orifice. Thus the theory of Torricelli is accurate when applied to the velocity that takes place at this section of the vein; but it cannot be true, at the same time, with respect to the mean velocity of the molecules which traverse the section of the orifice on account of the difference between the areas of these two sections. The velocity at the contracted section being known, the observation of the expanse of fluid in a given time will make us acquainted with the ratio of this section to that of the orifice, or with what is called the quantity of contraction, more exactly than can be done by direct measurement. The time is to be reckoned, and the quantity of liquid that flows out from a small orifice under a constant pressure is to be measured. At the same time, the quantity of liquid that ought to be discharged by the orifice is to be calculated by the rule of Torricelli. The ratio between the observed and calculated discharge will be a fraction which will express the quantity of contraction. This method, pointed out by D. Bernoulli, has been followed by M. Hachette. He neglected none of the precautions necessary to diminish the errors of experiment. He measured the time by means of a second watch of M. Breguet. The orifices which he employed were constructed and measured by M. Lenoir. By inspecting a communicating tube, he was always sure that the level of the fluid did not vary during the experiment; and, finally, his observations were made on a very large scale both with respect to the size of the vessel and the volume of water that flowed out, and likewise with respect to the time during which the liquid was flowing out, which sometimes amounted to more than an hour. A table placed at the end of his memoir gives the result of 28 experiments made in this manner on heights of water between 135 and 888 millimetres (5.315 and 34.96 inches), and with orifices varying from 1 to 43.3 millimetres (0.03937 to 1.626 inch). The smallest contraction observed by the author corresponds to the smallest diameter. It is 0.78. For diameters above 10 millimetres (0.3937 inch) the contraction becomes almost constant. It lies between 0.60 and 0.63. When the orifice remains the same, it increases a little with the height of the fluid; but it does not appear to depend upon the direction of the jet. Other philosophers who have determined the contraction of the vein differ from each other respecting its greatness. Newton, for example, considers it as 0.70; Borda found it 0·61; and in a certain case he found the area of the contracted vein reduced to almost one-half of the area of the orifice. No doubt this difference between such skilful observers ought to be partly ascribed to the size of the orifices, and to the pressures employed. But M. Hachette points out another cause which D. Bernoulli had already perceived, and which ought to have a notable influence on the quantity of contraction deduced from the waste of fluid observed. This cause is the form of the surface in which the orifice is pierced. According to M. Hachette, the waste of fluid (every thing else being the same) is the smallest when the surface in contact with the fluid is convex. It increases when the surface becomes plane, and still more when it becomes concave. Accordingly he observed that the waste varied about a twentieth part when the copper disc containing the orifice, and which is plane on one side, and a little concave on the other, was simply turned. M. Hachette proposes to continue his experiments on the flow of water through small orifices, varying all the circumstances which can have any influence on the flow in a given time, and endeavouring to find the laws of their influence. He proposes, likewise, to extend them to cylindrical vessels, emptied by great horizontal orifices. In that case the time of flowing out can no longer be determined by the theorem of Torricelli, which supposes the orifice very small. Its rigorous expression depends in each case on two transcendental quantities of the kind which Lagrange named functions gamma, and of which he has given very long tables in his Exercises on the Integral Calculus. By means of these tables we may calculate the time of flowing through an orifice whose diameter is any fraction whatever of that of the cylinder. This will enable us to compare theory with observation in this very important point of view, PART II.-Increase of the Flow by Cylindrical or Conical Tubes, This phenomenon was known to the Romans, though they were doubtless unable to appreciate it exactly. At the beginning of the 18th century, Poleni, Professor at Pavia, gave the measure of it in a very simple case, that of a cylindrical pipe of a length equal to about three times the diameter of the orifice. He showed that in that case the flow is increased one-third; so that if it amounts to 100 when the orifice is thin, it becomes 133 in the same time by the addition of the pipe. In a work published in 1797, M. Venturi, of Modena, has shown that by employing a pipe composed of a cylinder of a certain length, terminated by two cones whose dimensions he determined, the flow may be increased in the ratio of 12 to 5, or almost to 1 times as much as when the orifice is thin; and it does not appear that this philosopher obtained the maximum effect of which the pipes are capable; for M. Clement has been able to increase the flow considerably by changing the form of the VOL. X. N° I. C |